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Los Alamos scientists are figuring out how to do The date was February 4 th , 1975, and the setting was the city of Haicheng in northern China. On that day, the earthquake science commu- nity had a major breakthrough—for the first time ever, an earthquake of catastrophic proportions had been successfully predicted. Roughly a million people were evacuated beforehand and an untold number of lives were saved. There was just one problem: it was a fluke. The prediction was the result of a combina- tion of seismic rumblings (foreshocks), changes in well-water levels, and abnormal animal behavior. Based on these observations, state officials ordered a massive evacuation of Haicheng, and the next day a 7.3 magnitude earthquake shook the city, top- pling empty buildings and filling empty streets with rubble and debris. The prediction was lauded as an extraordinary achievement, and shortly there- after began the controversy. The methods failed to predict subsequent quakes and even 40 years later have yet to successfully predict another major earthquake. Faulty faults Earthquake scientists fall firmly into two camps: those who think all earthquakes are random events, caused by swirling thermal processes deep within the earth, and those who think that some quakes are actually triggered by others or are con- nected. Los Alamos geophysicist Paul Johnson is a member of the connected camp and believes that some earthquakes are triggered by seismic waves generated from far-off, previous earthquakes. He is 14 1663 April 2014 studying what he describes as a modulating effect, in which earthquakes that eventually would have happened anyway (thermal swirling) actually hap- pen sooner as a result of seismic perturbations from across the planet. By applying mathematical models and physical laboratory simulations, he and his collaborators want to understand how large earth- quakes change the physical properties of the earth’s crust and how these changes can lead to triggering of earthquakes in general—and temporal clustering of earthquakes in particular. “Since the last turn of the century there have been about 15 really large earthquakes,” Johnson says. “Are they all related?” He believes it’s likely they are, and he’s got the stats to back it. The surface of the earth, the watery and rocky layer within and upon which life exists, sits atop the deeper layers of crust and uppermost mantle, collectively referred to as the lithosphere. The earth’s brittle lithosphere is broken into eight major tec- tonic plates (as well as myriad smaller ones), which are the basis of plate tectonic theory, the theory describing global geophysical processes such as con- tinental drift and seafloor spreading. These plates are constantly moving and interacting, either sliding beneath one another in what is called subduction, or sliding past each other like opposing lanes of traffic in what is called lateral slipping. During these interactions, stress builds up along both sides of the fault (the interface of the two plates), and when the stress reaches a critical level, a slip event, or failure, occurs. If the failure is sudden, and the amount of built-up energy is large, an earthquake results.